


drink abundantly, O beloved

by nebulia



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Grinding, Idfic, Multiple Orgasms, Nonbinary Character, Nonbinary My Unit | Byleth, Oral Sex, Other, Overstimulation, Plot What Plot/Porn Without Plot, Religious Imagery & Symbolism, Rimming, Sacrilege, Sex as a sacred act, Squirting, They/Them Pronouns for My Unit | Byleth, Trans Character, Trans My Unit | Byleth, Wet & Messy, Worship, also i guess this is kind of, archive warning: a truly shameless number of religious metaphors for sex, but no religious guilt at all, everyone is v happy, no beta we die like Glenn
Language: English
Status: Completed
Published: 2020-08-29
Updated: 2020-08-29
Packaged: 2021-03-06 15:27:32
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 1
Words: 3,418
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26171161
Author URL: https://archiveofourown.org/users/nebulia/pseuds/nebulia
Summary: [Mercedes still prays to the Goddess, but it’s Byleth she worships.]I rose up to open to my beloved, and my hands dripped with myrrh, and my fingers with sweet smelling myrrh, upon the handles of the lock.
Relationships: Mercedes von Martritz/My Unit | Byleth
Kudos: 26





	drink abundantly, O beloved

**Author's Note:**

> no knowledge of Christianity is required to read this fic! i'm just using horny scripture and making baptism jokes. if you're familiar with the church of seiros you'll be fine.
> 
> presumably takes place in a non-crimson flower postcanon but there is no plot and no timestamp please don't ask i can't tell you
> 
> byleth is afab trans nonbinary, uses they/them pronouns, and uses prick, front hole, and cunt as terms for their genitalia (cunt both referring to the entire vulva as well as interchangeably with front hole). they have a mixture of short and tall byleth's features. because this is idfic, they have my ultimate iddy byleth headcanon: that the lace tights on short byleth are actually tattoos. deal with it. i am also afab trans nonbinary so i will fight you if you think i fucked this one up gender-wise.
> 
> references to the Goddess are explicitly references to sothis' gender & place within byleth and not Mercedes misgendering byleth. 
> 
> no beta because this is the iddiest of idfic! all mistakes are especially mine!
> 
> as always if this needs a tag I missed lmk!

_**sacrā̆ment** n.  
_ _1\. A sacrament of the Church, a visible sign imparting grace **  
** 2\. The sacrament of the Eucharist; the eucharistic elements, esp. the Host._  
_3\. Arcane knowledge; a secret; hidden significance, a mystery; a divine mystery; a mystery of religion.  
_ _4\. A solemn oath, pledge, covenant; also, a ceremony accompanying the taking of an oath or the making of a pledge._

Byleth is growing out their hair.

It suits them; softens their sharp jaw, framing their face. Their hair is finer than Mercedes’, almost fluffy, falling in layers around their chin and shoulders, and they love when Mercedes’ hands are in it, whether she’s playing with it or scritching along their scalp or tugging them between her legs.

Byleth was just as beautiful to Mercedes with short hair, as beautiful with blue-black hair as seafoam, but their own interest in their hair, the way it looks around their face, the way they smile when Mercedes combs it--Byleth _glows_ now, their shy, small smile coming out every time someone compliments it. Mercedes is growing her hair out again, too, and they compare--Mercedes’ is thick, already past her shoulders, and heavy. Byleth’s grows more slowly, finer, prone to wispy flyaways that Mercedes loves to twine around her fingers. Mercedes loves the way Byleth looks with it, the way it splays out around their head when Mercedes has them underneath her, a halo glowing light on the dark of their bedspread.

Byleth isn’t the Goddess; they’ve made that clear. The Goddess and Byleth were two separate entities, and have always been. But even if Byleth isn’t the Goddess’ soul, isn’t her spirit, the Goddess--Sothis herself--is _in them_ , and how many people get to say that the beloved deity that has guided their life is incarnate in the one they love? Mercedes feels like the luckiest human in the world. Who can be more beloved than her, to be loved so closely by Byleth?

Mercedes still prays to the Goddess; she was never interested in the cults of Seiros or any of the other saints. Her devotion was, and is, to Sothis, the Fell Star, and she has never felt she needed Seiros to intercede, though there was always a certain amount of tension in the Church with regards to the necessity of intercession. The more they uncover as they dig out the Church, the more she finds her religious practice drifting from the rituals of the Church of Seiros, becoming more personal. The cathedral--still half-caved in, as the treasury funds are needed elsewhere--has continued to be her place to pray, a sacred place newly made more holy in its wreckage, in the vigils held there during the war, in the grief and fear and pain left at the rubble like an offering at an altar. It is a place of the faith of people in a way it wasn’t when it was pristine before the war.

She still prays to the Goddess, but it’s Byleth she _worships._

Byleth is beautiful: taller than Mercedes and thick-shouldered with muscle from training with the sword and axe and brawling; small breasts with puffy nipples that grow hard every time Byleth unbinds their chest, sensitive to the softest whisper; the way the muscles in their chest and along their ribs narrow to a slim waist and long legs mottled dark and pale with the lace tattoos that run from hip to ankle; the lean lines of their thighs and ass; the sage-green of the hair, a few shades darker than the hair on their head, curling between their legs. Mercedes loves everything about them, whether their hair is blue-black or seafoam green, whether their eyes are the color of the grass or the sky. She’s not a poet, but Byleth makes her want to write hymns.

Byleth is beautiful and Mercedes kneels between their legs while they lay on the bed, blushing, tattooed thighs parting to reveal their cunt, already glistening in the candlelight. They’re pushed up on their elbows, watching her, and wisps of hair are already clinging to their jawline, where they’ve begun to sweat. Their hand reaches out, stroking Mercedes’ cheek, and Mercedes turns her head to kiss the inside of Byleth’s wrist, where their heart pounds, rabbit-fast, under thin skin.

“Mercedes,” Byleth whispers, eyes wide.

“Byleth,” Mercedes says, and Byleth shivers. They still get called _professor_ by nearly everyone, or _Your Grace_ when it’s official business, and when Mercedes calls them by name they’re always undone, and not just sexually. Hardly anyone has called Byleth by name since Jeralt died, not even Mercedes. It was inappropriate during school and felt strange during the war, especially when everyone else continued to call Byleth professor, but Mercedes has never been one for titles. The trappings of the Officer’s Academy, where “they were all equal,” delighted her, because she could call even the house leaders by name without official censure, and she enjoyed doing so with gusto. They were humans the same as she was.

Mercedes may call everyone by name, if she can get away with it, but calling Byleth by name still feels special, sacred. It feels like saying the name of a god no one else dares speak.

Mercedes dares. “Byleth,” she says again, mouth moving against Byleth’s wrist, and Byleth shudders again, more violently. “Byleth.” The name sounds like a prayer in her mouth.

Byleth makes a little noise, like a whimper, and Mercedes presses an open-mouthed kiss to their wrist, skimming her teeth along the vein to make Byleth _whine_. Their wrists are sensitive, and the line of their lower rib, and the cut of their hips. Mercedes knows every inch of Byleth in the way the formerly-censored scriptures of Cethleann describe knowing, but the scriptures never mentioned that it feels new every time. That every time Mercedes sucks a hickey into Byleth’s wrist, it’s like rediscovering a place she’s never been. Byleth throws their head back and Mercedes smiles against their skin.

“Mercie,” Byleth says, already breathless.

“Patience is a virtue,” Mercedes says sweetly, standing to remove her apron.

“I’m not virtuous,” Byleth says, rolling their eyes.

Mercedes folds her apron and drapes it across the clotheshorse. “Oh, my love,” she says, and unbuttons her shirt and unlaces her stays, untying her skirt, kicking off her drawers, leaving only her chemise. “You very much are.” She kneels between Byleth’s legs again, and grins up at them, knowing Byleth is looking at her nipples, visible through the nearly-sheer fabric of her chemise. “A paragon of virtue, even.”

Byleth’s blush spreads down their neck. “Mer _cedes_.”

Mercedes laughs, and leans in to taste the sweat at the crease of Byleth’s inner thigh, nosing against the curls of Byleth’s pubic hair, before taking one long lick up Byleth’s cunt, tasting them salty and tangy, smiling against their prick when she hears them gasp, thighs tensing around her. She sucks Byleth’s prick gently, for only a moment, before dropping down to lap at their opening, to taste them from the source, coax still more slick from them.

“ _Oh_ ,” Byleth says, low-voiced, and Mercedes hums against their skin, hoisting one of Byleth’s heavy thighs over her shoulder before Byleth drapes their remaining over Mercedes’ other shoulder themself, hips canting up. Mercedes licks them, lightly for a few moments before she sinks her tongue in while she reaches up to touch Byleth’s prick, hard and tight, barely peeking out of its hood, with her thumb. She strokes lightly for a moment, and then pulls to lick her thumb and when she presses against Byleth’s prick again she pushes a little harder, her saliva easing her rhythm, rubbing up and down in a tight oval as she licks into Byleth.

Byleth’s pelvis kicks up and Mercedes grips their hip with their free hand, not holding them down, but easing them into a rhythm she can handle as she eats them out and pulls them off at the same time. Her senses are full of Byleth: of their smell, their taste, their low moans, the feeling of their muscles flexing against Mercedes’ hand as they move in a sinuous writhe against her mouth, picking up in pace and desperation as they get closer and closer to coming. Their heels thud into Mercedes’ back, holding her fast against them, thighs clenching around her head, and she can feel the way they get wetter, before she distantly hears them say, “I’m gonna, oh, fuck-- _Mercie_ \--” and they come, their slick becoming thicker, taste heavier in Mercedes’ mouth as they kick her again with their heels, hips bucking.

It might bruise, but Mercedes doesn’t mind so much. She pulls her mouth away, Byleth’s come already thick enough to be stringy, to watch Byleth come, but keeps rubbing their prick until they shies away, saying, “Too much, hang on--” and sighing when Mercedes pulls her thumb away from the hard nub, stroking their slick folds gently instead of pulling away completely. Byleth makes a questioning noise, slumped back on the bed and gasping for air.

“I’m not done with you yet,” Mercedes says, and spreads Byleth’s cuntlips open, their hole open and slippery and prick still hard. “You can go again, can’t you?”

“Yeah,” Byleth says, and then: “ _Gently_.”

“Always,” Mercedes says, and kisses their lacy thigh before sinking her teeth in hard enough to bruise.

“Hey!” Byleth says, but their voice isn’t nearly as protesting as Mercedes thinks they’d like to be. She didn’t miss how Byleth’s hips jerked at the bite. “That’s not _gently.”_

Mercedes smooths the bite with a kiss. “Sorry, love,” she says, and kisses the spot, already bruising a little. She brushes her thumb across Byleth’s open front hole as she kisses the spot again. “Is this better?”

“Mmm. _Please_ ,” Byleth says, and stretches their arms out above them, languorous. Mercedes watches them and burns, her thighs slick with her own arousal, but making Byleth come, watching Byleth come, tasting Byleth come, gets her closer than anything else.

She presses her thumb into Byleth’s front hole, pulling it to gape just enough to push her tongue inside, to drink deeply of Byleth, nose nudging their prick, and then her tongue slides lower, pulling one ass cheek aside, hand sunk deep in the muscle, to reveal their asshole, surrounded by sparse green hairs. When she touches her tongue to it, Byleth whines, and Mercedes bends her thumb, pressing its knuckle into the spongy tissue of the upper wall of their cunt while she licks Byleth’s asshole until it begins to open under her mouth, until she can press her tongue against the furl of it and taste soap and sweat and musk.

“ _Fuck!”_ Byleth says, and Mercedes sucks on the hole until Byleth loses their breath before licking again, more firmly, long flat laps across the crinkled skin, dragging her thumb in and out of Byleth’s front hole. When Byleth’s breaths pick up speed, she presses again, tongue pushing against the adit, just barely pressing inside as it relaxes around her.

Byleth whimpers, and Mercedes licks deeper, rubbing her the knuckle of her thumb against that spot along their inner wall with unyielding pressure, almost rough if not for how wet Byleth was, how slick their cunt is. She’s rewarded when Byleth’s sounds go high-pitched and wounded, desperate, heels thumping against Mercedes back as their hips kick again and again. They twitch violently as they come another time, this time with a gush of thin, salty fluid that mostly ends up on Mercedes’ face, in her mouth. She gulps it down, feels it clump on her lashes, rivulets running down her throat. It’s really not much liquid, but it’s enough to wreck Mercedes. Enough to christen her.

“That’s it, sweetheart,” she says into the skin of Byleth’s ass cheek, and pulls her thumb out to slip two fingers in and _crook,_ pressing harder. “Want to give me more?”

Byleth cries out and does, this time gushing into Mercedes’ mouth, across her cheeks. Mercedes swallows what she can, more come dripping off her face, and Byleth spurts once more, this time splattering Mercedes’ throat and chest, consecrating the light fabric of her chemise and turning it totally sheer, clinging to her hard nipples and breasts.

Goddess. Mercedes can barely breathe, the pressure of her own thighs against her cunt unbearable. She can’t help herself when she leans in and presses her mouth to Byleth’s cunt, their twitching prick, and _sucks_ , their brackish ejaculate, their pungent slick, the hallowed, sacred taste cc of Byleth that only Mercedes gets to know.

Byleth makes a high, hurt noise, hips twitching away from her, as they tremble under Mercedes’ mouth. Mercedes rips herself away and strokes down Byleth’s cunt, their taint, with careful fingers.

“I’m sorry,” she says breathlessly. “I just--” She can’t finish, because she’s watching her index finger, wet with spit and come and slick, slide into Byleth’s asshole with almost no resistance, watching Byleth’s hips arch. “You are so…” Mercedes doesn’t have a word for Byleth like this. There aren’t words for this in a human language. “Can I give you another, love? Byleth?”

Byleth sighs, rocking back onto Mercedes’ finger. “Mm--think so,” they slur, and Mercedes pulls away for a moment to push Byleth further back on the bed so she can get on the bed too, between their legs, tucking her own heel against her cunt to rub off on it. Byleth’s hair is soaked moss-green from sweat. “Mercie...feels good--”

“You deserve to feel good,” Mercedes says, and frames their prick with two fingers, jerking the hood gently, careful not to touch the oversensitive nub, while she pushes two fingers into their ass. “I want to give that to you.” Pay it to Byleth, like a tithe, like an offering. Worship them, be baptized by them, be blessed by them--Mercedes wants Byleth to know they have everything of her. She rubs Byleth off, fucking their ass with a deliberately slow rhythm, fingers curved just so, and it doesn’t take as long as Mercedes expects for Byleth to arch their back and say “ _Oh--”_ their eyes popping open in surprise as they come again. They don’t squirt, but with their legs spread wide for Mercedes she can see the way their open cunt slicks more, the curls of their pubic hair soaked, their thighs wet and shining.

“Fuck, Mercie,” they breathe, and move to sit up, but Mercedes pulls her hands away and reaches up and pushes them back down.

“Let me give you one more,” she says. She pops the fingers that jerked Byleth off into her mouth, tasting them--more out of desire than provocation--and watches Byleth’s eyes dilate as they widen.

“Mercie, I can’t, I’m--”

“I think you can,” Mercedes says, and taps Byleth’s cunt with her hand. Byleth spasms, so wet that the gentle impact makes them splatter, and Mercedes licks that hand, too turned on to care how desperate she herself looks. “I know you can,” she says, looking up at Byleth. “I’ve got you.” She pushes one of Byleth’s thighs up, swirls a damp finger around a lace filigree tattoo at random before pressing their leg against her shoulder and turning to kiss their calf as she rucks her chemise up around her waist and straddles their hips, settling her cunt against Byleth’s still-hard prick and beginning a slow rock. The wetness between them makes a filthy squelching noise that has Mercedes’ ears getting hot and Byleth’s blush spreading blotchy across their chest.

“M-mercie,” Byleth stutters, head pressed back hard against the bed, eyes shut tight. “Mercie, oh f-ff _fffuck--”_

 _“_ Shhhh,” Mercedes says, and leans down to press a kiss to Byleth’s sweaty jaw, rocking Byleth’s prick against the slickest part of her cunt. She won’t come like this--not enough consistency, not enough pressure--but Byleth will, oversensitive and trembling, the two of them wet enough that the slide of their prick between them is near frictionless, and watching Byleth come is a holy experience. Mystical. Ecstatic. She picks up the pace and Byleth gasps and nearly thrashes beneath her, almost dislodging her. 

Mercedes adjusts Byleth's leg so it's hooked over her elbow and leans down to kiss Byleth's cheek. “That’s it, Byleth,” she says against their jaw. “Goddess, but you’re gorgeous.” She’d like to bite their earlobe but doesn’t think she has the coordination, not when they’re both this close.

Byleth’s hips jerk under her, and then they make a keening, desperate wail in the back of their throat and come, wet between them, slicking both their thighs and spilling onto the bedspread.

They’re still coming even after they finish ejaculating, thighs shaking under Mercedes, and Mercedes lowers Byleth’s leg and adjusts so she’s riding Byleth’s thigh, spreading her own cuntlips with two fingers so her clit makes contact with Byleth's sweaty thigh. The glide is easy with her own slick and Byleth’s come, and she braces herself with her knee pressing into Byleth’s twitching cunt, against their prick. She rocks down, hard, the pressure just right--she’s close, and Byleth convulses underneath her, the pressure of her knee unrelenting. Mercedes presses her cunt down, grinding her clit into the muscle of Byleth’s thigh, and watches the sweat between on their breastbone sliding to pool in the hollow of their throat, their mouth open and drooling, their eyes trying to focus on her but rolling away, tears streaking into their matted lichen hair, sticking to their ears and neck as they toss their head against the bed. They’re trying to speak, but all that comes out of their mouth are desperate, half-aspirated gasps, the _mmmmph_ they make when they try to say Mercedes’ name but bite their lip to muffle a shriek instead. Their hands fist in the bedspread, and Mercedes has never seen anything more sacred than Byleth, coming and coming and coming apart in Mercedes’ hands. She rocks down hard, her head falling back, and comes. “Byleth,” she says to the heavens. “Byleth, Goddess, _Byleth--_ ”

When she takes in a full breath again, Byleth is panting underneath her, still shaking. Mercedes climbs off them and uses the already wet bedspread to wipe between both their thighs before flopping down next to them, chemise still bunched around her waist, draping an arm and a leg over Byleth’s sweaty body, pushing up just enough to press a kiss under their ear, and then another, and then a leave a hickey just to have the taste of Byleth’s skin.

“Mercedes,” Byleth says finally, voice hoarse. “Everyone says you’re sweet, but only a villain would make me come four times in half an hour.”

Mercedes laughs, and rolls onto Byleth, her regrowing hair a curtain around the two of them. “Mm. Yes. A villain who loves you.”

Byleth’s arms come around Mercedes’ waist and they pull her down into a hug. “I love _you_ ,” they say. “You never--you always.” They pause, and Mercedes glances up at their face. “You treat me like me. Not a goddess, not a demon. Both and neither.” They sigh. “I don’t know how to say it. I’m not good at words.”

“You are perfect, even being both and neither,” Mercedes says, and reaches up to kiss their chin. “I love you because you’re you. You having the Goddess in you is just a bonus. I’ve been blessed twice over.”

Byleth huffs a laugh, cheeks pink. “How so?”

Mercedes kisses their chin again. “I got you,” she says, and shifts a little so she can reach to kiss their jaw. “ _You_ , Byleth. Gentle and kind and patient and fierce. That would have been enough. I would never have needed more than you. But _then_ \--” she kisses the corner of their mouth-- “My Goddess lives in your heart. Who could be more blessed than me?”

“Me,” Byleth says quietly, and tangles their fingers in Mercedes’ hair to push their mouths together, uncaring of where Mercedes’ mouth has been. “It’s me.” They kiss Mercedes again, and again, and again.

Mercedes pulls away. “Don’t think kissing me will distract me from arguing about this with you--mmph!” Byleth kisses her again, their mouth opening wetly against hers, their fingers smoothing her hair, their sticky legs tangled with Mercedes’. Human and Goddess both; not just Mercedes’ deity, but her human too, snarky and sweet and smelling like sweat and souring sex.

Mercedes can let them win.

_Then will I pour clean water upon you, and ye shall be clean._

**Author's Note:**

> title: Song of Songs 5:1 (KJV)  
> summary: Song of Songs 5:5 (Jubilee 2000)  
> front epigraph: shamelessly chopped and screwed from the [Middle English Dictionary](https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary)'s definition of "sacrament"  
> back epigraph: Ezekiel 36:25 (Geneva 1599)
> 
> Behold! I have listened to that ancient fandom proverb and have written what I wanted to see in the world!
> 
> if you don't think there's some cethleann-penned song of songs equivalent seteth has banished to the shadow library i don't know what to tell you. either way there are, canonically, cethleann devotee-penned song of songs equivalents in the shadow library, so.
> 
> comments and kudos are always appreciated!!!
> 
> you can find me most often at [coaIsack](http://twitter.com/coaisack) on twitter!


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